Polycrystalline samples hot-pressed with Al, B, and C sintering additions (ABC-SiC) were characterized by using transmission electron microscopy. The study focused on the effects of high-temperature treatment on microstructure. Three temperatures, at which considerable microstructural changes took place, were found to be critical. At a threshold temperature of approximately 1000C, 1nm-wide, amorphous intergranular films started to crystallize. At approximately 1300C, lattice diffusion in SiC grains resulted in nano-precipitates, which could diffuse into grain boundaries and significantly altered composition there. Quantitative micro-analysis revealed doubled Al content in intergranular films after annealing at 1300C. Except for crystallization in intergranular films and nano-precipitation in matrix grains, microstructure remained stable until 1600C, at which microstructural changes with volatile features occurred. A brief holding at 1900C brought marked changes in microstructure, including structural change in intergranular films, dissolved nano-precipitates, unit cell dilation, and cracking. The results indicated that ABC-SiC was highly promising in structural applications at up to 1500C.

Thermal Modification of Microstructures and Grain Boundaries in Silicon Carbide. X.F.Zhang, L.C.De Jonghe: Journal of Materials Research, 2003, 18[12], 2807-13